Rubella virus (RV) is a human pathogen and the causative agent of German measles. RV infection during the first trimester of pregnancy can cause fetal death or mutisystem birth defects. Histopathological analysis of several tissues of infants with congenital rubella syndrome revealed generalized growth retardation, possibly due to mitotic inhibition. Further, a mitotic inhibitory factor has also been identified from the RV-infected cells. To understand the mechanisms of RV induced growth inhibition, we will identify cellular factors that are responsible for alteration in cellular growth following RV infection. In addition, we seek to understand how natural RV infection or immunization alters the function of cellular factors. We have characterized host-encoded proteins that interact with the cis-acting elements of RV RNA that are essential for replication. One of the host proteins that has been identified is a homologue of human calreticulin. Calreticulin is a phosphoprotein and is hyperphosphorylated upon RV infection. The phosphorylation site(s) has(have) been localized in the N-terminal domain of calreticulin and its interaction with RV RNA is dependent upon phosphorylation. The phosphorylation of calreticulin in uninfected cells is dependent on the state of cell cycle. To define the role of calreticulin in RV replication, we have developed Vero cell lines (CR-1) which over-express calreticulin. Surprisingly, RV replication is significantly reduced in CR-1 cells. However, there is no alteration in binding of calreticulin to RV RNA from such cells. Flowcytometeric analysis of synchronized CR-1 cells showed that a high proportion of cells arrested in S phase and upon RV infection they persist in S phase. To understand the mechanism by which over-expression of calreticulin alters cell cycle and inhibits RV replication, we are analyzing the factors that regulate cell cycle and the mechanism such factors control RV replication. Characterization and identification of cellular factors that are necessary for viral pathogenesis may provide clues for the cause of RV vaccine associated complications and provide necessary information for the improvement of future RV and other childhood vaccines.Publication: C. D. Atreya, G. P. Pogue, N. K. Singh, H. L. Nakhasi (1996) Role of Calreticulin in Rubella Virus Replication In Calreticulin, Molecular Biology Intelligence Unit (Ed) Marek Michalak. Springer, R. G. landes Company pp 89-111